The primary aim of this study is to define the effect of the number of natalizumab cycles on development of brain atrophy and progression of disability in originally treated patients with natalizumab in relapsing multiple sclerosis (MS).

The secondary objective of this study is to define the effect of the number of natalizumab cycles on accumulation of T2-LV and T1-LV and their VW-MTR changes over 5 years.